As a driving section for driving a load such as a motor of a fuel pump mounted on a vehicle, a DC drive or a pulse modulation drive such as a PWM (Pulse Width Modulation) control is used. And, the operational state of the fuel pump can be controlled by suitably selecting the DC drive, the pulse modulation drive or a stop operation depending on vehicle conditions.
Since the load cannot be suitably driven if the switching element has a trouble, various technologies have been proposed in order to prevent the trouble of the switching element. As a cause of the trouble of the driver (switching element), an overcurrent flowing in the switching element can be considered. As another cause, a case where the temperature of the circuit becomes high can be considered. As the overcurrent is occurred in the switching element, the temperature of the circuit naturally increases. And thus, the trouble of the motor is caused and a suitable preventing means is required.
For example, as a technology for detecting an overcurrent of the motor in order to protect the switching element from a failure due to the overcurrent of the motor, as illustrated in FIG. 1, there is a technology that detects an electric current flowing in the switching element. A FPCM (Fuel Pump Control Module) 110a is a device for controlling the driving of the motor 160 of the fuel pump and includes a MCS (Motor Control System) 120 and an IPS (Intelligent Power Switch) 130. The IPS 130 includes a driver 135 and a self-diagnostic output circuit 140. The driver 135 includes a high side-transistor 131 which is a P channel MOSFET and a low side-transistor 132 which is an N channel MOSFET. And, the MCS 120 drives the motor 160 in the PWM drive by switching the high side-transistor 131 and the low side-transistor 132 using a PWM control. When the motor is driven in the DC drive, the MCS 130 maintains the high side-transistor 131 in the on-state and the low side-transistor 132 in the off-state.
Further, the self-diagnostic output circuit 140 includes a current detecting function for detecting an electric current flowing in the high side-transistor 131 of the driver 135 and a error detecting function for detecting an occurrence of an error. The current detecting function of the self-diagnostic output circuit 140 is adapted to output, for example, one of several thousand of an electric current flowing in the high side-transistor 131. A predetermined resistance is provided between the output part of the current detecting function and a ground part. Also, as a MCS 120 detects a voltage on an output part side of the current sensor function of the resistance, it is determined whether an overcurrent flows in the motor or not.
As another technology, as indicated in the FPCM 110b shown in FIG. 2, there is a technology in which an overcurrent of the driver 135 is estimated by detecting a temperature thereof using a temperature detecting circuit 170 arranged in the vicinity of the IPS 130. Further, in an applied technology for the technology of FIG. 2, restricting values of the electric current are set in a stepwise fashion (for example, Patent Document 1).    Patent Document 1: JP-A-2007-228704